Microsoft Entra Connect sync stopped, request upgrade and library not found

Please try this:

1. Check for Inconsistent Installer Packages

• Open %ProgramData%\AADConnect\ and inspect the latest installation trace log.
• Look for entries like GetInstalledPackagesByUpgradeCode to identify if older versions are still registered.
• If the wizard detects remnants of older installations, it may trigger the upgrade button unnecessarily.

2. Manually Remove Corrupt Install Entries

• Use msiexec /x {ProductCode} to uninstall any ghosted or partially removed packages.
• Be cautious, do not edit the registry directly unless guided by Microsoft support.

3. Reinstall Microsoft Entra Connect Cleanly

• Download the latest version from the  official Microsoft Entra Connect page.
• Uninstall the current version completely.
• Reboot the server.
• Install the new version and reconfigure sync.

4. Verify .NET and Dependencies

• Ensure that the required .NET Framework version is installed and healthy.
• Use sfc /scannow to check for system file corruption.

5. Check for DLL in NuGet or SDK

• The missing DLL (Microsoft.IdentityModel.Clients.ActiveDirectory.dll) is part of the Azure AD Authentication Library (ADAL).
• You can manually download it from  NuGet and place it in the expected path, but this is a workaround and not officially supported.